Extraction of potassium from the clay fraction of a bentonite

Electro-ultrafiltration (EUF) method was employed at 20, 40 and 80 degrees C for investigation of potassium extraction from a K+-saturated <2 mu m fra ction of a bentonite. Up to 85% of total potassium present in the sample wa s extracted. At least three different sites of K+ desorption were found on bentonite particles dispersed in water. EUF analyses of duration of 30-40 m inutes were optimal for adequate information on K+ sites. Experiments at 20 degrees C and voltages 50-350 V caused desorption of K+ from the external surface of particles, which terminated after extraction of about 9 mg K/g c lay, i.e. 22% of total potassium present. Increase in voltage to 400 V appl ied at 20 degrees C caused onset of K+ desorption from the weaker interlaye r sites, observed also at 40 degrees C and 50-150 V. These sites are suppos ed to occur mainly in swelling interlayers of smaller quasicrystals, close to the layers of lower negative charge. At 200 V started K+ desorption from the stronger interlayer sites, occurring probably predominantly in the les s swelling interlayers of bigger particles, next to highly charged layers. As expected, no sharp border appears between the weaker and stronger interl ayer sites, they cover combined 63% of total potassium present in the inves tigated material.